1. Field of the Invention
This invention relates to the diffusion of zinc into indium phosphide or into ternary or quaternary III-V systems based on indium phosphide.
2. Description of Related Art
In the manufacture of light sources and detectors for use in telecommunications, the quaternary system indium gallium arsenide phosphide has been extensively used. One of the reasons for this is that an indium gallium arsenide phosphide/indium phosphide double heterostructure laser has an emission wavelength which coincides with a low loss regime in silica based optical waveguides.
In the manufacture of indium gallium arsenide phosphide/indium phosphide devices such as lasers, LEDs and photodetectors, a commonly used process step is to diffuse zinc into the structure. In a laser, for example, the zinc diffusion provides a low resistance path from a subsequently formed laser top contact to a laser active region.
The zinc diffusion, which typically takes place at 500.degree. C. for a period of about 2 hours, degrades the substrate surface. In particular phosphorus loss causes etch pits to appear on the crystal surface and these pits detract from crystal integrity of subsequent epitaxial growth. In an attempt to reduce surface damage it is known to diffuse zinc in the presence of phosphorus vapour. However if the partial pressure of phosphorus is too high, there is minimal zinc diffusion.